JPS58143216A - Slope meter of water surface - Google Patents

Abstract

PURPOSE:To obtain a slope meter of water surface having high accuracy, by conducting water by pipes to one place from two points of the up and down streams and detecting the difference of water level. CONSTITUTION:Tanks 1, 2 in which sand is sunk disposed at two points of the up and down streams at a distance of the length L of a section where the water level is measured, are connected to a pressure tank 5 by water conducting pipes 3, 4. The air in the tank 5 is evacuated by a suction pump 6 and the water in the tanks 1, 2 are sucked up, and floats 7, 8 are connected to a differential gear mechanism 9 by a pulley, and the difference of water level is converted to a rotation angle of the differential gear and is detected by a potentiometer or an encoder.

Description

[Detailed Description of the Invention] Recently, there has been a strong demand for more sophisticated river water management such as flood forecasting and water use adjustment, and there is an increasing need for improved accuracy and automation of river flow measurement.

Methods using current meters and floats are generally used to measure light gravity in open waterways such as rivers, but these methods both require human labor and cannot continuously measure flow rates.

Ultrasonic current meters have been experimentally used as automatic flow rate measurement devices in open channels, but in actual rivers, the results have not been very good due to irregular cross-sectional shapes and the effects of turbid water during floods. It has not been done.

Therefore, in order to continuously measure the flow rate, the widely adopted method is to continuously measure the water level and convert it to flow rate using a water level-flow curve. Under changing conditions, the water level by flow observation -
The preparation of the flow rate curve requires a period of several months to a year, which does not satisfy the demands of management problems that require immediate flow rates. Furthermore, the water level-flow rate curve itself does not hold at points where the water surface gradient changes independently of the water level, such as upstream points of tidal areas, movable weirs, and upstream points of confluence points.

On the other hand, gauging weirs and partial flumes can be used in small waterways, but this method is often not available in rivers and large waterways because it is difficult to install such facilities.

By the way, the flow rate Q is the product of the flow rate i and the cross-sectional area A: Q=A-1・
・・・・・・・・・・・・・・・・・・・・・(1), and the flow velocity V is a constant roughness coefficient as represented by the Manning formula % formula %(2) Since it is calculated by the diameter depth R and the water surface gradient (2), which are determined as a function of the n5 water level, if the water surface gradient is continuously measured in addition to the water level, the flow velocity and flow rate can be continuously calculated.

Water surface slope I is the water level difference △H between two points upstream and downstream of an open channel divided by the length of the section, so ■=ΔH/L ・
・・・・・・・・・・・・・・・・・・・・・・・・(3
) Mathematically, it is sufficient to install water level needles at two points upstream and downstream, measure the water level, calculate the difference, and divide by the length of the section, but from a measurement perspective, this method This is an effective result because the measurement range is wide compared to the difference, the relatively large water level measurement error and the difficulty in maintaining the relative positional relationship between two upstream and downstream points greatly affect the measurement accuracy of the water level difference. It can't fly.

*The length of the section varies depending on the measurement accuracy of Δ1■ and the maximum value of the water surface gradient to be measured, but in reality it is between 30 and 2007
It is #.

This invention is a water surface gradient meter that is characterized by ensuring high measurement accuracy by detecting the water level difference between two water surfaces formed in one place by introducing water from two points upstream and downstream using a single detector. This is what we are trying to provide.

In the figure, 1 and 2 are sand settling tanks installed at two points, upstream and downstream, separated by a distance of 1 the length of the water level measurement section, and connected to the pressure tank 5 by water guide pipes 3 and 4. The pressure tank 5 forms an inverted siphon, and the air inside is reduced in pressure by a suction pump 6 to suck up water from the upstream and downstream sediment tanks. 7 and 8 are two floats floating on the water surface in the pressure tank, which are connected to the differential gear mechanism 9 by a pulley, and the water level difference is converted into the rotation angle of the differential gear, which is detected by a potentiometer or encoder. .

Here, if the change in the flow of the open channel is slow enough, hydrostatics can be applied to the water in the sand settling tank, water guide pipe, and pressure tank, so atmospheric pressure Po1 air pressure in tank P5 upstream water level H1% downstream Water level H2, tank upstream water level H1',
When the downstream water level in the tank is H2/, the following relationship holds true.

Pa +H1w P +1(1'・・・・・・−・
...-(4)Po + H2= P +HX...
・・・・・・・・・・・・・(5) (4) formula − (5) formula Hl−)]2= H1'−H2' ==△H・Old・・
(6) That is, regardless of the values of atmospheric pressure Po and tank air pressure P, the water level difference between two water surfaces in the tank is equal to the water level difference between two upstream and downstream points.

Regarding the detection of the water level difference in the tank, the double float method shown in the figure achieves a high accuracy of 0.1%, but the differential pressure gauge method can also easily ensure an accuracy of 0.5 inches.

The biggest problem when measuring water levels in large waterways such as rivers is the cancellation of short-period waves such as wind waves and dynamic water pressure, but with the device of this invention, this can be easily canceled by the friction of the pipe. In addition, the removal of earth, sand, garbage, sludge, etc. that cause difficulties in maintenance and management can be dealt with by rationally designing the structure of the settling tank, and by periodically inspecting and cleaning it.

The features of the device of this invention are as follows.

(1) The flow rate can be measured without affecting the flowing water of an open channel, such as by raising the weir with a weir or restricting it with a flume.

(2) Since it is based on hydraulic formulas, flow velocity and flow rate can be calculated using roughness coefficients for which empirical values have been accumulated and cross-sectional area, diameter depth, and cross-sectional characteristics.

(3) Hydraulic knowledge such as roughness coefficients can be accumulated through calibration work such as flow rate observation.

(4) High accuracy can be ensured because the maximum value of the water level difference is set to the full scale, and maintenance is easy because there is no need to pay special attention to maintaining the reference height of the upstream and downstream water inlets.

(5) Since the facility is civil engineering/mechanical, it is easy to maintain by river engineers and its operation is highly reliable.

(6) Can be used for the entire range of river flow rates, from low water to rotten water.

(7) It can also be used in locations where forward or reverse currents occur, such as in tidal areas.

(8) If the suction method is used as a water conveyance method, it is easy to install and maintain pressure tanks and water conveyance pipes, it is easy to prevent and remove earth and sand, and water can be conveyed reliably in times of low water. effective.

If the water surface gradient meter of this invention is used in conjunction with a water level meter and a recently advanced microcomputer is utilized, flow rates can be automatically and continuously measured, recorded, and displayed at river sites, etc. This will have a tremendous effect on water use adjustment and flood forecasting, which require the flow of water, and will enable total automation of river water management systems for the first time. Ota,
Significant labor savings can also be expected in flow rate observation work for survey purposes, which has traditionally required a large amount of manpower on each river.

The device of this invention is needed as a water supply at points where the water level and water surface gradient change independently, such as tidal areas, upstream points of movable weirs, and upstream points of confluence points, but it can also be used in general rivers and irrigation channels. In reality, there are many cases where the water surface slope changes with the water level, so the use of the device of this invention can be expected to improve flow measurement accuracy and save labor, and is particularly effective in measuring flood peak flow in small rivers with rapid flow. is very large.

[Brief explanation of the drawing]

The figure shows the basic mechanism of the present invention, which pumps up water using pipes from two points up and down an open channel and generates a water level difference to be measured in a pressure tank installed at a central point.

Claims (1)

[Claims] Measure the water level difference between two static water surfaces obtained by conveying water from two points upstream and downstream to the midpoint of an open channel with a pipe along the flow direction, and divide it by the distance between the two points upstream and downstream to calculate the flow rate. A water surface gradient meter characterized by determining the water surface gradient.